1. Field of the Invention
The present invention relates to a technique for inspecting whether an irregular defect or a color defect is generated on a surface of an object to be inspected which is formed of a material having a high regular reflectance (a resin, metal or the like).
2. Description of the Related Art
It is very important for a product which places a particular emphasis on its design such as a car or a home appliance to have no irregularity in luster or color on its surface in view of enhancing its commercial value.
Although a surface of such product is made of a colored resin or metal, the surface could have an irregular defect or a color defect.
The irregular defect is generated when the surface is protruded or recessed caused by a manufacturing defect. The irregular defect includes a scratch generated after manufactured. The color defect is generated when a peripheral coating material is attached on the surface at the time of manufacturing.
As a method of detecting the above defect by using an image processing method, Japanese Unexamined Patent Publication No. 2003-75363 discloses that a surface of an object to be inspected (referred to as the “work” hereinafter) is irradiated with a coaxial incident illumination and an illumination from an oblique direction, and a first imaging device for taking an image of a regularly reflected light from the work with respect to the coaxial incident illumination, and a second imaging device for taking an image of a diffused reflected light from the work with respect to the illumination from the oblique direction are provided. In addition, an irregular defect on the surface of the work is detected using the image generated by the first imaging device, and a color defect on the surface of the work is detected using the image generated by the second imaging device.
However, according to the method in Japanese Unexamined Patent Publication No. 2003-75363, since the two imaging devices are provided, the cost becomes high. In addition, they occupy a large space in an optical system, and control for the imaging devices individually is complicated.
Furthermore, according to Japanese Unexamined Patent Publication No. 2003-75363, the cylindrical work to be inspected is rotated and each imaging device takes an image of an entire periphery of the work, and each region whose image is to be taken is sequentially irradiated with two kinds of illuminations. According to this method, a processing time is long, so that many works cannot be processed efficiently.